Human immunodeficiency virus (HIV) is the etiological agent of Acquired Immune Deficiency Syndrome (AIDS). There are two types of HIV currently recognized, HIV-1 and HIV-2. HIV-1 is the predominant form worldwide. There are three HIV-1 groups, the major group (M group), the outlier group (O group), and the non-M/non-O group (N group). The M group is further divided into at least eleven distinct genetic subtypes that are commonly referred to as subtypes or clades: A, B, C, D, E, F, G, H, I, J, and K. Subtype B is the most prevalent in the United States, while subtype C is the most prevalent worldwide. Geographic distribution of genetic subtypes is continually changing, and current data offers incomplete estimates.
Approximately 95% of new HIV infections occur in developing countries, thus a vaccine may be the most effective way to control the epidemic. However, developing effective vaccines to inhibit, reduce, or neutralize HIV infection has been a difficult challenge to the scientific community. It is a primary goal to develop an HIV vaccine that can effectively elicit broad and balanced anti-viral immunity, including protective antibody responses, and in particular, neutralizing antibody (NAb) and cell-mediated immune responses to control the spread of HIV. The extraordinary degree of genetic diversity of HIV has been problematic for vaccine development.